Robert Jung is building a second home for his family. He just hopes they never will have to use it. Mr. Jung is a member of Weiterfuhrender Selbstschutz Verein (Club for Further Measures of Self-Protection). While tens of thousands march in the streets of West Germany to protest the presence of nuclear weapons, much smaller numbers - like the 40 in Jung's club - react to the nuclear threat in a much different way: They make plans to survive.
''The people think it is chic to be a member of Greenpeace and Amnesty International,'' Jung says. ''They go and tell their friends, to make an impression, but they do no work. We make it clear in our speeches that this is work.'' The club's work is the construction of a shelter deep inside a mountain. Tentative plans are for a shelter that would accommodate 3,000 people, providing for all of their basic needs and protection from all types of hostility for several years.
Jung, a railroad engineer, is a believer in bunkers. ''My parents built a shelter in the last war,'' he recalls. ''My mother, brother, two neighboring families, and a few Russian prisoners used it - about 20 people. It saved our lives.'' Jung has been concerned about the possibility of another war. ''I knew the government program for protection was not adequate for a big catastrophe,'' he says.
Then one evening he and his wife attended a lecture in their hometown of Hassloch. The speaker was Karl Rohner, architect for the city of Freinsheim. By day, he supervises reconstruction of historic structures and gives advice to village residents who are putting up new buildings. But on evenings and weekends , Mr. Rohner works devotedly on the shelter project. The biggest part of that these days is spreading the Weiterfuhrender Selbstschutz message, and that is not an easy job.
''People don't like to hear this,'' Rohner says. ''Many people want to be jolly and refuse to face their responsibilities; they flee into festivals.''
Rohner has given his series of three lectures several times over the last three years, speaking in about 20 cities and villages in southwestern West Germany.
''This was the first time,'' Jung recalls, ''that someone came and showed a way to withstand this type of war.''
Not surprisingly, the idea of bunkering in for nuclear (or biological or chemical) war is an emotional one. Many who hear Rohner's speeches reject the idea out of hand, because it is such an unpleasant topic. Others object on grounds of cost. The shelter builders are in a distinct minority in West Germany today. The peace movement has aimed some of its indignation at the concept, with banners like ''Who is building shelters is thinking of war,'' and ''Who is building shelters also throws bombs.''
Even Rohner's family is divided over the issue. His wife, Eva, isn't involved in club business. ''She does not like to think of defending the shelter,'' he says, noting that it might be necessary to shoot any nonmembers attempting to storm the shelter as members are entering. ''She also does not like to think of what will be necessary afterwards.'' The couple's only child, Ellen, 25, is even more ideologically at odds with Mr. Rohner. Ellen is not a member of the radical Green party, but she considers her views similar to the Greens.
''I think he is crazy,'' says Ellen, a student in West Berlin. ''I think we must try to do something to prevent war, not dig bunkers and try to survive it.''
Jung's family is more in agreement. Jung's wife attended the Rohner speech with him and also favored joining the club. Then they showed their children, ages 15, 10, and 9, the club's plans.
''We explained everything when asked,'' Jung says. ''Their reaction was that they were very astonished that other parents do nothing for their children.''
Rohner's message is stark and jolting. He speaks of another war - not as a possibility, but as nearly inevitable. While many of his countrymen are protesting the United States deployment of Pershing II missiles in West Germany, Rohner does not look on the Pershings as a particular threat to peace. What he sees as a threat are various changes in the world that he believes will make conflict more likely. Among these:
* The emergence of new superpowers. Rohner feels Communist China is on the verge of arriving at superpower status with the US and Soviet Union. Rohner also considers Brazil capable of reaching that status by virtue of its population and resources, and he regards a union of Europe under one government as possible. Such a European union would have superpower status.
With two superpowers, he says, there is only one possible conflict. With three superpowers, seven different conflicts are possible; with four superpowers , there are 36 conflict combinations; with five, 171.
* The completion of nuclear armament in China by 1984. ''Both American and Russian papers have announced this,'' Rohner says. ''The Chinese capacity may be enough to eliminate Russia as an industrial nation.''
* Laser stations in space. By the end of this decade, Rohner says, the race will have begun between the US and the USSR in the construction of antinuclear space stations. If one country gets a large lead in the race, Rohner is concerned that the country that is behind will attack the other out of fear for its own security.
* A growing shortage of strategic resources. As world demand rises, oil and certain metals will become even more scarce than they are now. Economic development - and a lot of military equipment - may depend on availability of resources.
* Acts of terrorism. Rohner says Pakistan has borrowed money from Libya and Algeria in order to stockpile 50 nuclear warheads a year. Pakistan being a poor nation, Rohner says, it is likely to repay the debt - not in money - but in bombs.
''These are the developments possibly leading to war,'' Rohner says. ''It is very unlikely to succeed in avoiding all of them . . . , so we think it is inevitable to do what we are convinced to do.''
A bookshelf along one wall in the office in Rohner's home here in Ungstein is dominated by books about modern warfare, balance of world power, and trends of the future. Filling one shelf are 11 thick binders of materials he has collected , from which he has worked out in detail what would be needed in each facet of building and living in the underground shelter.
Attempting to survive a nuclear war is a chilling thought. In America there is a great deal of debate about whether any structure would offer an adequate shelter from the effects of nuclear war - and whether after a large-scale nuclear conflict there ever would be a habitable environment to emerge into. But for those who share Rohner's determination to try to protect their families and to survive modern warfare, Rohner has an alternative: to go underground. His plan calls for a shelter that would accommodate hundreds of people for 41/2 years.
The planning begins with the entrances. An important requirement is that they provide for decontaminating vehicles, people, and animals before they enter the main shelter. Bacteriological and chemical weapons are a possibility Rohner has anticipated. They are in many cases more deadly than nuclear radiation and do not have some of the drawbacks, such as extended contamination and physical destruction.
To combat bacterial and chemical contamination, airlocks are planned for each entrance. Once inside the first set of doors, a vehicle would be treated to decontaminate it in the appropriate manner.
An adjoining entrance is wide enough to permit cattle to enter. Animals and people would walk through a shallow pool to decontaminate hooves and shoes.
In their air lock, people would put on clean clothing. After they were decontaminated, the second set of doors would be opened to permit them into the main part of the shelter. Entrance to the living and working quarters is gained through a long tunnel.
The tunnel would be deliberately weakened in two places; if an invading army tried to enter the shelter, a charge could be set off that would block the tunnel with several yards of rock. That option would be a last resort. Farther out, the tunnel has a bottleneck where it could be sealed quickly by several yards of soft silicon foam that bullets could not penetrate. TV monitors in the tunnel would permit guards to watch for intruders from a control room deep within the shelter. Switches to open the gates (and activate the foam or tunnel-blocking explosives) would be operated pneumatically, making them invulnerable to the electromagnetic pulse (EMP) caused by atom bombs. This pulse , it is theorized, could ruin any electronic devices it reached. In fact, Rohner plans an EMP-proof room in which to store computer tapes and other items that would be vulnerable.
Air would enter the shelter through a system of tubes reaching out toward the earth's surface. These tubes wouldn't extend to the surface, but would stop in trenches several feet deep. The trenches would be nearly filled with gravel, then covered with enough topsoil so that grass could be grown to disguise their location.
Water would come from an underground vein. In the particular site Rohner has found, the vein is situated diagonally around the site, permitting water to be taken from the higher part of the vein and sewage to be routed into the lower part to be carried away. The sewer would be an open canal with a narrow walkway alongside it. Food would be stored in dried and canned form in small rooms in the shelter. This would be sufficient for survival, but provisions would also be made for some fresh food to give variety to the diet. Greens would be grown in a large interior hallway under artificial light. Special rooms would house cattle and chickens, in order to allow each inhabitant occasionally to have milk and eggs.
Facilities for medical care would be part of the shelter, and Rohner plans to recruit medically trained people.
But mere survival is not the sole goal of the shelter. While waiting for the bombs to stop falling and for the radiation to dissipate, people would have work to do. ''Each person must learn some kind of handwork,'' says Rohner. A variety of skills must be represented in the group so that a wide range of services be available, as the members try to rebuild after they come out of the shelter.
In addition to learning a skill, each able-bodied adult will be expected to work an eight-hour shift: cleaning, repairing, guarding, recycling, cooking, tending animals. The biggest job would be digging to complete a new exit tunnel, presuming it was necessary to completely block the original one. Rohner considers meaningful work vital to the survival of the inhabitants. He say, ''We can't just go down there and sit.'' The community would even have its own newspaper and school.
A control room would maintain contact with the outside world by monitoring broadcasts, if any. When radiation returned to levels thought to be safe, workers would come out to begin the next project: planting crops.
First, three or four inches of topsoil would be peeled off with bulldozers to avoid use of contaminated soil. Then glass houses would be put up to protect crops from any additional radiation. Seed would be grown in the shelter so that enough is available for a second planting in case the first year's crop fails. Inhabitants would come out of the shelter with the equivalent of two suitcases full of possessions per person.
The work on Rohner's plan is scheduled to begin immediately, he says. He has found a potential site near Kallstadt, the next village down the road from his hometown of Ungstein. A geologist offered his services gratis and pronounced the site nearly ideal.
The land belongs to the village. Soon Rohner will ask the 15-member city council for permission to use the land. If they vote favorably, construction may begin.
''The club can vote to begin construction at any time,'' Rohner says. He offers this scenario:
The 40 members vote to chip in an average of 3,000 marks ($1,200) each. The physical labor each must pledge to construction of the shelter when they join the club can be considered to add one-third to the value of the cash investment. This means, Rohner says, the club can qualify for a loan of 640,000 marks, which in all would provide enough, Rohner estimates, to build the entrance gate and 25 meters of tunnel. If the shelter is built to accommodate 3,000 people, it would cost about 75 million marks ($30 million) - 25,000 marks ($10,000) a person. The per capita cost would rise for a smaller shelter.
A major factor in the shelter's financing is the concept of an ''economic zone.'' This is a part of the shelter that would be rented out as office or work space for everyday use in peacetime. The club would receive rent from the business use of this portion of the shelter (which is also inside the area considered safe from a direct strike of a 1 megaton bomb), and the people who worked there would have protection in event of a sudden attack. When the shelter is completed and paid for, the rent from businesses would be rebated to the members.
So far, Rohner says, there is only one large shelter in West Germany. It's located in Bavaria and could accommodate 100 people. Another architect in Frankfurt has plans similar to Rohner's.
Switzerland, Rohner says, already has large shelters that would accommodate 700,000 people, 13 percent of its population. West German shelters would hold only 0.2 percent. France and Great Britain have built similarly infinitesimal numbers of shelter.